1. Field of the Invention
The following description relates to a mobile communication system, and more particularly, to a method for setting a scheduling information triggering condition for efficiently managing a common Enhanced Dedicated Channel (E-DCH).
2. Discussion of the Related Art
First, a Universal Mobile Telecommunications System (UMTS) to which the present invention is applied is described as follows.
FIG. 1 illustrates a network structure of the UMTS.
The UMTS system mainly includes a User Equipment (UE), a UMTS Terrestrial Radio Access Network (UTRAN), and a Core Network (CN). The UTRAN includes one or more Radio Network Sub-systems (RNSs) and each RNS includes a Radio Network Controller (RNC) and one or more base stations (Node Bs) managed by the RNC. One Node B has one or more cells.
FIG. 2 illustrates a wireless (or radio) protocol structure used in the UMTS.
Pairs of wireless protocols, which are present in the UE and the UTRAN, are responsible for transmitting data in wireless intervals. Each wireless protocol layer will now be described. First, a physical (PHY) layer, which is the first layer, functions to transmit data in a wireless interval using various wireless transmission technologies. The PHY layer is responsible for reliable data transmission in wireless intervals. The PHY layer is connected to a MAC layer, which is a higher layer, through a transport channel. The transport channel is classified into a dedicated transport channel and a common transport channel according to whether the channel is shared or not.
The second layer includes Medium Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP), and Broadcast/Multicast Control (BMC) layers. The MAC layer is responsible for mapping various logical channels to various transport channels and is also responsible for logical channel multiplexing to map various logical channels to a single transport channel. The MAC layer is connected to the RLC layer, which is a higher layer, through a logical channel. The logical channel is mainly classified into a control channel used to transmit control plane information and a traffic channel used to transmit user plane information, according to the type of transmitted information.
The MAC layer is further classified into a MAC-b sublayer, a MAC-d sublayer, a MAC-c/sh sublayer, a MAC-hs/ehs sublayer, and a MAC-e/es or MAC-i/is sublayer, according to the type of managed transport channel. The MAC-b sublayer is responsible for managing a broadcast channel (BCH) which is a transport channel responsible for broadcasting system information. The MAC-c/sh sublayer is responsible for managing a common transport channel such as a forward access channel (FACH) which is shared with other UEs. The MAC-d sublayer is responsible for managing a dedicated channel (DCH) or an enhanced dedicated channel (E-DCH) which is a transport channel dedicated to a specific UE. In order to support high-speed uplink and downlink data transmission, the MAC-hs/ehs sublayer manages a high-speed downlink shared channel (HS-DSCH) which is a transport channel for high-speed downlink data transmission and the MAC-e/es or MAC-i/is sublayer manages an enhanced dedicated channel (E-DCH) which is a transport channel for high-speed uplink data transmission.
The RLC layer is responsible for guaranteeing a QoS of each radio bearer (RB) and transmitting data according to the QoS. The RLC has one or two independent RLC entities for each RB in order to guarantee the inherent QoS of the RB and provides three modes, a transparent mode (TM), an unacknowledged mode (UM), and an acknowledged mode (AM), in order to support various QoSs. The RLC serves to adjust the size of data so as to be suitable for a lower layer to transmit the data in a wireless interval. To accomplish this, the RLC also functions to split and connect data received from a higher layer.
The PDCP layer, which is located above the RLC layer, allows data to be efficiently transmitted in a wireless interval with a relatively small bandwidth using an IP packet such as IPv4 or IPv6. To accomplish this, the PDCP layer performs a header compression function which allows only indispensable information to be transmitted in a data header, thereby increasing the efficiency of transmission in wireless intervals. The PDCP layer is present mainly in the PS domain since the header compression is a basic function. One PDCP entity is present for each RB in order to provide an efficient header compression function for each PS service. The PDCP layer does not provide the header compression function when it is present in the CS domain.
The second layer also includes a broadcast/multicast control (BMC) layer above the RLC layer. The BMC layer functions to schedule cell broadcast messages and to perform broadcasting to UEs located in a specific cell.
The Radio Resource Control (RRC) layer, which is located at the bottom of the third layer, is defined only in the control plane. The RRC layer is responsible for controlling first and second layer parameters in association with setup, reset, and release of RBs and for controlling logical, transport, and physical channels. The RB is a logical path that the first and second layers of the wireless protocol provide for data transfer between the UE and the UTRAN. Setup of an RB is generally a process for defining characteristics of wireless protocol layers and channels required to provide a specific service and for setting their respective specific parameters and operating methods.
The following is a more detailed description of the E-DCH.
The E-DCH is a transport channel dedicated to a single UE which is used to transmit uplink data to a Node B in the UTRAN. In order to transmit data at a high rate, the E-DCH uses technologies such as Hybrid ARQ (HARQ), Adaptive Modulation and Coding (AMC), and Node B controlled scheduling.
For the E-DCH, the Node B transmits downlink control information, which controls E-DCH transmission of the UE, to the UE. The downlink control information includes acknowledgement information (ACK/NACK) for HARQ, channel quality information for AMC, and E-DCH transmission power allocation information for Node B controlled scheduling, or the like.
On the other hand, the UE transmits uplink control information to the Node B. The uplink control information includes E-DCH UE buffer status information for Node B controlled scheduling, UE power status information, the size of payload indicated by an E-TFCI, retransmission count, UE power surplus status report, or the like.
E-DCH transmission of the UE is controlled by the Node B. The E-DCH control of the Node B is performed by a scheduler which is responsible for allocating optimal radio resources to each UE. Specifically, the scheduler allocates a large amount of radio resources to a UE that is in a good radio channel condition and allocates a small amount of radio resources to a UE that is in a bad radio channel condition so as to reduce interference in the uplink radio channel.
The scheduler allocates radio resources taking into consideration not only the radio channel condition of the UE but also information such as the amount of available power that the UE can use for the E-DCH or the amount of data that the UE desires to transmit. That is, the scheduler allocates optimal radio resources to a UE, which has remaining power for the E-DCH and also has data for transmission in uplink, taking into consideration the radio channel condition.
Accordingly, to transmit data through the E-DCH, first, the UE notifies the Node B of the amount of power available to the UE and the amount of data for transmission. The amount of available power and the amount of data for transmission of the UE are transmitted through Scheduling Information (SI), a detailed structure of which is illustrated in FIG. 3.
FIG. 3 illustrates a structure of the scheduling information.
The following is a description of parameters included in the scheduling information as shown in FIG. 3.
UE Power Headroom (UPH) indicates the ratio of the amount of power that the UE currently uses to the maximum amount of power available to the UE and thus indicates the amount of available power that the UE can use for the E-DCH.
Total E-DCH Buffer Status (TEBS) indicates, in bytes, the total amount of data of the UE awaiting transmission in the RLC and MAC layers. TEES indicates the total amount of data using an index in the range of 0 to 31 as illustrated in the following Table 1.
TABLE 1IndexTEBS value (bytes)0TEBS = 01 0 < TEBS = 10210 < TEBS = 14314 < TEBS = 18418 < TEBS = 24. . .. . .3028339 < TEBS = 376423137642 < TEBS
For example, the TEBS is set to 0 (TEBS=0) if the total amount of data of the UE awaiting transmission is 0 byte and is set to 29 (TEBS=29) if the total amount of data is 29 bytes.
Highest priority Logical channel Buffer Status (HLBS) indicates the ratio of the amount of data of a highest priority logical channel to the total amount of UE data for transmission. Specifically, the HLBS indicates an index corresponding to 100×(the amount of highest priority logical channel data/the total amount of UE data for transmission).
Highest priority Logical channel ID (HLID) indicates the highest priority logical channel among logical channels having data for transmission.
The UE should transmit the scheduling information only in a specific condition for efficient use of radio resources instead of transmitting the scheduling information each time. To accomplish this, 3GPP currently defines the following conditions for triggering generation of scheduling information.
TABLE 2Scheduling information Triggering Conditionswhen new data for transmission is generated in UE.when data for transmission is generated in logical channel with higherpriority than logical channel in which data awaiting transmission ispresent.when HARQ transmission of MAC PDU including data and schedulinginformation has failed.when a predetermined time is reached at regular intervals.
When scheduling information is generated when one of the triggering conditions is satisfied, the UE transmits a Medium Access Control Packet Data Unit (MAC PDU) including the scheduling information to the Node B. The MAC PDU generally includes higher-layer data and scheduling information. The MAC PDU may include scheduling information alone when higher-layer data is absent. The generated MAC PDU is transmitted to the Node B through a HARQ process in the MAC layer.
If the UE notifies the Node B of UE power and data status through scheduling information, the scheduler of the Node B determines the amount of power available to the UE for E-DCH transmission taking into consideration the status of the UE and the entire radio status of the cell and notifies the UE of the determined amount of available power through a downlink control signal. The downlink control signal notifying the UE of the amount of power is classified into two types, an Absolute Grant (AG) indicating an absolute value of the amount of power available to the UE and a Relative Grant (RG) indicating a value of the amount of power available to the UE relative to the amount of previously used power. Upon receiving the AG or RG downlink control signal, the UE determines the amount of power for use in E-DCH transmission and determines the size of a MAC PDU for transmission according to the determined amount of power.
On the other hand, the 3GPP standard defines a common Enhanced Dedicated Channel (common E-DCH) to allow a number of UEs to commonly use the E-DCH under control of the Node B.